UndefBranchChecker.cpp revision a1f81bb0e55749a1414b1b5124bb83b9052ff2ac 
1//=== UndefBranchChecker.cpp -----------------------------------*- C++ -*--===//
2//
3//                     The LLVM Compiler Infrastructure
4//
5// This file is distributed under the University of Illinois Open Source
6// License. See LICENSE.TXT for details.
7//
8//===----------------------------------------------------------------------===//
9//
10// This file defines UndefBranchChecker, which checks for undefined branch
11// condition.
12//
13//===----------------------------------------------------------------------===//
14
15#include "ClangSACheckers.h"
16#include "clang/StaticAnalyzer/Core/Checker.h"
17#include "clang/StaticAnalyzer/Core/CheckerManager.h"
18#include "clang/StaticAnalyzer/Core/PathSensitive/CheckerContext.h"
19#include "clang/StaticAnalyzer/Core/BugReporter/BugType.h"
20
21using namespace clang;
22using namespace ento;
23
24namespace {
25
26class UndefBranchChecker : public Checker<check::BranchCondition> {
27  mutable OwningPtr<BuiltinBug> BT;
28
29  struct FindUndefExpr {
30    ProgramStateRef St;
31    const LocationContext *LCtx;
32
33    FindUndefExpr(ProgramStateRef S, const LocationContext *L)
34      : St(S), LCtx(L) {}
35
36    const Expr *FindExpr(const Expr *Ex) {
37      if (!MatchesCriteria(Ex))
38        return 0;
39
40      for (Stmt::const_child_iterator I = Ex->child_begin(),
41                                      E = Ex->child_end();I!=E;++I)
42        if (const Expr *ExI = dyn_cast_or_null<Expr>(*I)) {
43          const Expr *E2 = FindExpr(ExI);
44          if (E2) return E2;
45        }
46
47      return Ex;
48    }
49
50    bool MatchesCriteria(const Expr *Ex) {
51      return St->getSVal(Ex, LCtx).isUndef();
52    }
53  };
54
55public:
56  void checkBranchCondition(const Stmt *Condition, CheckerContext &Ctx) const;
57};
58
59}
60
61void UndefBranchChecker::checkBranchCondition(const Stmt *Condition,
62                                              CheckerContext &Ctx) const {
63  SVal X = Ctx.getState()->getSVal(Condition, Ctx.getLocationContext());
64  if (X.isUndef()) {
65    // Generate a sink node, which implicitly marks both outgoing branches as
66    // infeasible.
67    ExplodedNode *N = Ctx.generateSink();
68    if (N) {
69      if (!BT)
70        BT.reset(
71               new BuiltinBug("Branch condition evaluates to a garbage value"));
72
73      // What's going on here: we want to highlight the subexpression of the
74      // condition that is the most likely source of the "uninitialized
75      // branch condition."  We do a recursive walk of the condition's
76      // subexpressions and roughly look for the most nested subexpression
77      // that binds to Undefined.  We then highlight that expression's range.
78
79      // Get the predecessor node and check if is a PostStmt with the Stmt
80      // being the terminator condition.  We want to inspect the state
81      // of that node instead because it will contain main information about
82      // the subexpressions.
83
84      // Note: any predecessor will do.  They should have identical state,
85      // since all the BlockEdge did was act as an error sink since the value
86      // had to already be undefined.
87      assert (!N->pred_empty());
88      const Expr *Ex = cast<Expr>(Condition);
89      ExplodedNode *PrevN = *N->pred_begin();
90      ProgramPoint P = PrevN->getLocation();
91      ProgramStateRef St = N->getState();
92
93      if (PostStmt *PS = dyn_cast<PostStmt>(&P))
94        if (PS->getStmt() == Ex)
95          St = PrevN->getState();
96
97      FindUndefExpr FindIt(St, Ctx.getLocationContext());
98      Ex = FindIt.FindExpr(Ex);
99
100      // Emit the bug report.
101      BugReport *R = new BugReport(*BT, BT->getDescription(), N);
102      bugreporter::trackNullOrUndefValue(N, Ex, *R);
103      R->addRange(Ex->getSourceRange());
104      R->disablePathPruning();
105
106      Ctx.EmitReport(R);
107    }
108  }
109}
110
111void ento::registerUndefBranchChecker(CheckerManager &mgr) {
112  mgr.registerChecker<UndefBranchChecker>();
113}
114